Numerous bags or sachets are known, for example but not exclusively for household use, that are fitted with assemblies at their mouths for making it possible at will to open them and close them several times in succession.
Such closure assemblies are known in particular that comprise two support webs carrying respective complementary male/female elements facing each other at the mouth of the bag. Functionally equivalent closure assemblies are also known that comprise hooks on the webs for being positioned facing one another at the mouth of the bag for fastening together by hooking onto one another.
In other fields, in particular in the fields of providing displays or wrapping, sheets are also known that are fitted with fastener assemblies designed to cooperate with complementary fastener assemblies or means provided on another sheet or on an associated support.
The applicant has found that under certain circumstances prior fastener or closure assemblies do not give complete satisfaction.
This applies in particular to fastener or closure assemblies made out of polyolefins, mainly polyethylene or polypropylene. After being extruded, and prior to being secured to films for making up sheets or bags, such assemblies are generally wound on circular reels for storage purposes. Unfortunately, the polymers used for this purpose have elastic memory of their conditions of transformation, and over time they recrystallize, passing through various phases and in the form of different types of crystallite.
This leads to high levels of internal tension causing the assemblies that are stored in this way on circular reels to be subjected to a kind of warping or curling.
Such curvature can be very troublesome when implementing the process of securing fastener or closure assemblies on the film that is to constitute sheets or a bag. It will really be understood that because of this warping or curling of the assemblies, it is very difficult to ensure that such fastener or closure assemblies are accurately rectilinear after being unwound from storage on a reel. As a result, in use, it can sometimes be difficult to put such complementary fastener or closure assemblies in position, and consequently it can be difficult to obtain proper closure of bags or satisfactory assembly of sheets. Furthermore, it is often necessary to guide the assemblies so as to bring them onto the film that is to make up the bags or the sheets prior to securing them thereto, in particular when the fastener or closure assemblies are conveyed in a direction that extends across the travel direction of the film. It can turn out that if the fastener or closure assemblies are badly warped, then they can escape from the guides.
Various solutions have already been proposed consisting in particular in applying twisting to such closure assemblies in the direction opposite to that which was applied during storage, so as to eliminate the memory effect. Reference on this point can be made in particular to U.S. Pat. No. 6,616,881.
Nevertheless, that solution does not give full satisfaction.